Question

How to write 4 different functions that check if a number is a power of 2 in Kotlin

Answer 1

import kotlin.math.roundToInt

object PowerOfTwoCheck {

    // Method A: Bit‑counting
    fun isPowerOfTwoA(x: Int): Boolean {
        if (x <= 0) return false
        return x.toString(2).count { it == '1' } == 1
    }

    // Method B: Bitwise trick
    fun isPowerOfTwoB(x: Int): Boolean =
        x > 0 && (x and (x - 1)) == 0

    // Method C: Repeated division
    fun isPowerOfTwoC(x: Int): Boolean {
        if (x <= 0) return false
        var n = x
        while (n % 2 == 0) {
            n /= 2
        }
        return n == 1
    }

    // Method D: Using logarithms
    fun isPowerOfTwoD(x: Int): Boolean {
        if (x <= 0) return false
        val logv = kotlin.math.log2(x.toDouble())
        return kotlin.math.abs(logv - logv.roundToInt()) < 1e-10
    }

    @JvmStatic
    fun main(args: Array<String>) {
        val test1 = 16 // true
        val test2 = 18 // false

        println("A: ${isPowerOfTwoA(test1)}, ${isPowerOfTwoA(test2)}")
        println("B: ${isPowerOfTwoB(test1)}, ${isPowerOfTwoB(test2)}")
        println("C: ${isPowerOfTwoC(test1)}, ${isPowerOfTwoC(test2)}")
        println("D: ${isPowerOfTwoD(test1)}, ${isPowerOfTwoD(test2)}")
    }
}



/*
OUTPUT:

A: true, false
B: true, false
C: true, false
D: true, false

*/

 

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